Adaptive laser conditioning of reflective thin film based on photo thermal lens probe.

A novel laser conditioning (LC) concept that performs adaptive control of exposure fluence is proposed. As photo-thermal absorption effect can discover defects responsible for laser-induced damage of reflective thin film, in situ photo-thermal lens probe is introduced in conventional LC procedure to detect defects during raster-scanning. The absorptance signal is fed back to guide the adaptive control of exposure fluence. By this method, the damage risk accompanying with LC can be reduced to a rather low level. In order to test the performance of adaptive laser conditioning (ALC), an experimental setup has been built, and several film samples have been tested. The results show that ALC is effective at reducing laser damage risk.